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Comment by lukifer | Hacker News Reader

When discussing the idea that our universe is simulated, often the assumption is that it's an experiment by aliens or somesuch. But recently I've started to wonder if our parent universe is nearly identical to our own, and we are one of millions of virtual Earths used for political and economic predictions, because if (when) we could, that's exactly what we would do.

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If true, this has an interesting implication - if our parent universe bothers to do it, it probably means they get useful information from it. That means that the recursion eventually terminates, that eventually in some great great grandchild universe they are able to produce the seed of the answer to whatever the original question was, rather than start another simulation.

My intuition is that the recursion shouldn't hurt getting useful results, even if the simulation was allowed to proceed past the point where such a simulation was developed (which they may not have), in a manner akin to the resolution of Zeno's Paradox. Though there's likely a bound on how many layers deep we can go, but my quantum information theory isn't what it used to be so I have to hand wave my conjectures.

> Though there's likely a bound on how many layers deep we can go

Yes. The universe only has so much computing power, and any universe we simulate will have less.

Does this depend on the universe having a finite amount of mass or what?

http://en.wikipedia.org/wiki/Bekenstein_bound

Thanks. Any recommended books for a soft introduction to these concepts?

Programming the Universe by Seth Lloyd (physics professor at MIT who likes to call himself a "quantum mechanic").

Here's a relevant paper by Lloyd titled "Ultimate physical limits to computation": http://arxiv.org/abs/quant-ph/9908043v3

That would apply to real-time simulations. But wouldn't every layer run successively slower? The inhabitants wouldn't notice how fast their simulation is running in the (grand)parent universe. So given infinite time the layering could be infinitely deep.

If the recursion spawns an average of more than one child universe per parent universe, then it would spawn an infinite number of universes, and maybe this is still the first run which, to the disappointment of our unknown benefactors, will produce no useful information.

It could also simply be monitored for CPU usage, and have the process auto-terminate when spiked by recursive children. Creating our own Virtual Earth might then destroy the universe. :P

Another disturbing thought: if our universe were spun up or down like we do virtual machines, would we even notice?

if our universe were spun up or down like we do virtual machines, would we even notice?

I would guess not. See Permutation City by Greg Egan for lots of speculation about questions like that.

I imagined I had given some thought to these subjects, but Permutation City did have new ideas. If you slow down a simulation to some ridiculous degree, the simulated beings don't notice. Even if you run the simulation backwards or in random order, they wouldn't notice. If you abruptly shut it down, they'll just continue finding the pattern somewhere.

http://qntm.org/responsibility

Good read, thanks.

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